1. Field of the Invention
The present invention relates to a positive resist composition.
This application claims priority from Japanese Patent Application No. 2004-98184 filed on Mar. 30, 2004, the disclosure of which is incorporated by reference herein.
2. Description of the Related Art
In the production of semiconductor devices and light crystal display devices, fine working has rapidly advanced, recently with progress in lithography techniques. A light source having a shorter wavelength is generally employed for fine working. Specifically, ultraviolet rays typified by g-rays and i-rays have conventionally been used, but now KrF excimer laser (248 nm) and ArF excimer laser (193 nm) have been introduced.
As one of the resist materials which satisfy the conditions of high definition capable of reproducing a pattern having a fine size, for example, there is known a chemically amplified resist composition comprising a base resin and an acid generator generating an acid under exposure, which are dissolved in an organic solvent, wherein alkali solubility changes due to an action of an acid generated from the acid generator.
As the base resin component of the chemically amplified resist, for example, there can be used polyhydroxystyrene (PHS) having high transparency to KrF excimer laser (248 nm), PHS resin wherein a portion of hydroxyl groups of PHS are protected with an acid dissociable dissolution inhibiting group and a copolymer derived from a (meth)acrylate ester. As the acid generator, for example, onium salt-based acid generators such as iodonium salt and sulfonium salt are now used most popularly.
As the organic solvent, for example, propylene glycol monomethyl ether acetate (which hereinafter referred to as PGMEA), ethyl lactate (which hereinafter referred to as EL), methyl amyl ketone (which hereinafter referred to as MAK) and propylene glycol monomethyl ether (which hereinafter referred to as PGME) are used alone or in combination. However, when these solvents are used alone, there arise a problem that a base resin may be agglomerated in a resist composition.
As the solvent mixture, a solvent mixture of PGMEA and EL (which hereinafter referred to as EM) is used most popularly because it is excellent in the effect of inhibiting agglomeration of the base resin (see, for example, Patent Document 1). It is considered that the effect of inhibiting agglomeration of the base resin in the solvent mixture such as EM is exerted because polarity of the entire organic solvent changes by mixing two kinds of solvents having different polarities.
As a method capable of forming a resist pattern having a high aspect ratio with high resolution, for example, a two-layer resist method using a chemically amplified resist has been proposed (see, for example, Patent Documents 2 and 3). According to this method, an organic film as a lower resist layer is formed on a substrate and then an upper resist layer is formed thereon using a chemically amplified resist containing a silicone resin as a base resin. After forming a resist pattern on the upper resist layer by a photolithography technique, the resist pattern is transferred to the lower resist layer by etching using the resist pattern as a mask to form a resist pattern having a high aspect ratio.
Patent Document 1: Japanese Patent Application, First Publication No. 2003-167364
Patent Document 2: Japanese Patent Application, First Publication No. Hei 6-202338
Patent Document 3: Japanese Patent Application, First Publication No. Hei 8-29987
However, when the resist pattern is formed by using the chemically amplified resist containing the silicone resin, there arise problems such as line width roughness (LWR) wherein the upper portion of the resist pattern has roundness and the line pattern has non-uniform line width, and line edge roughness (LER) wherein the side wall of the line pattern has irregular surfaces, and thus the resulting pattern has poor shape. With the recent increase of demand for high definition, it becomes important to solve the problems of the shape such as LWR and LER.